Press-forming method

ABSTRACT

Provided is a press-forming method including three steps for preventing spring-back in a hat-shaped cross section shape of a final formed article. In the first step, from a blank, a preformed article in a first form is obtained, the preformed article including a top surface, left and right vertical walls, and left and right tapered portions extending outward from lower ends of the left and right vertical walls, respectively, of a final formed article having a hat-shaped cross section. In the second step, the compression can be applied to the entirety of the top surface, the left and right vertical walls, and the left and right flanges of the final formed article having the hat-shaped cross section, whereby the spring-back can be sufficiently prevented. In the third step, obtain the final formed article having the hat-shaped cross section.

This application is based on and claims the benefit of priority fromChinese Patent Application No. 202210305026.1, filed on 25 Mar. 2022,the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a press-forming method.

Related Art

A technique has been proposed for obtaining, from a plate-like blank, afinal formed article having a hat-shaped cross section by press-forming,the final formed article including a top surface, vertical wallscontinuing to both ends of the top surface, left and right flangesextending from lower ends of the vertical walls, and bent portionsinterposed between the vertical walls and the flanges (for example, seeJapanese Unexamined Patent Application, Publication No. 2017-42791).

Patent Document 1: Japanese Unexamined Patent Application, PublicationNo. 2017-42791

SUMMARY OF THE INVENTION

In the technique disclosed in Japanese Unexamined Patent Application,Publication No. 2017-42791, the following two forming steps are providedwhen the formed article including the flanges bent in a longitudinaldirection at a pair of vertical walls in the hat-shaped cross section isobtained by press-forming. In the first forming step, the flange to besubjected to a shrinkage flange deformation is formed to be short in aline length in the longitudinal direction, and the flange to besubjected to a stretch flange deformation is formed to be long in a linelength in the longitudinal direction. In the second forming step, afinal formed article is formed using a mold with a product shape. Thus,it is considered that spring-back can be reduced. However, according tothe technique disclosed in Japanese Unexamined Patent Application,Publication No. 2017-42791, even when compression is applied to theflanges and local portions in the vicinity thereof, it is difficult toapply compression to the entirety of the top surface, the verticalwalls, and the flanges. Therefore, the effect of preventing thespring-back is limited.

The present invention has been made in view of the circumstancesdescribed above, and is to provide a press-forming method capable ofsufficiently preventing spring-back by applying compression to theentirety of the top surface, the vertical walls, and the flanges in thehat-shaped cross section of the final formed article.

(1) The present invention provides a method of press-forming, from ablank (for example, a blank 2 to be described below), a final formedarticle (for example, a final formed article 1 to be described below)having a hat-shaped cross section and including a top surface (forexample, a top surface 3 to be described below), left and right verticalwalls (for example, a left vertical wall 4 and a right vertical wall 5to be described below) continuing to left and right ends of the topsurface, left and right flanges (for example, a left flange 6 and aright flange 7 to be described below) extending from lower ends of theleft and right vertical walls, respectively, and left and right bentportions (for example, a left bent portion 8 and a right bent portion 9to be described below) interposed respectively between the left verticalwall and the left flange and between the right vertical wall and theright flange, the press-forming method including: a first step (forexample, a processing step corresponding to a phase P1 to be describedbelow) of obtaining, from the blank, a preformed article in a first form(for example, a preformed article 30 in a first form to be describedbelow) including the top surface, the left and right vertical walls, andleft and right tapered portions (for example, a left tapered portion 31and a right tapered portion 32 to be described below) extending outwardfrom the lower ends of the left and right vertical walls, respectively;a second step (for example, a processing step corresponding to a phaseP2 to be described below) of forming the left and right bent portionsby, in a state where the top surface of the preformed article in thefirst form is held by an upper die (for example, a second upper die 14to be described below) and a punch (for example, a floating punch 16 tobe described below) of a lower die (for example, a second lower die 15to be described below), pushing the left and right tapered portions intorecesses for curling forming (for example, a left recess 17 and a rightrecess 18 to be described below) provided in the lower die, and formingthe left and right flanges by lowering of the upper die to obtain apreformed article in a second form (for example, a preformed article 40in a second form to be described below); and a third step (for example,a processing step corresponding to a phase P3 and a phase P4 to bedescribed below) of obtaining the final formed article having thehat-shaped cross section by reforming the left and right bent portionsand the left and right flanges of the preformed article in the secondform.

In the press-forming method according to (1) described above, thepreformed article in the first form is obtained from the blank in thefirst step, the preformed article including the top surface, the leftand right vertical walls, and the left and right tapered portionsextending respectively outward from the lower ends of the left and rightvertical walls in the final formed article having the hat-shaped crosssection. In the second step, the left and right tapered portions arepushed into the recesses for curling forming provided in the lower diein the state where the top surface of the preformed article in the firstform is held by the upper die and the punch of the lower die, therebyforming the left and right bent portions, and the left and right flangesare formed by the lowering of the upper die to obtain the preformedarticle in the second form. In the third step, the left and right bentportions and the left and right flanges of the preformed article in thesecond form are reformed to obtain the final formed article having thehat-shaped cross section. In the course of obtaining the preformedarticle in the second form in the second step, the compression can beapplied to the entirety of the top surface, the left and right verticalwalls, and the left and right flanges of the final formed article havingthe hat-shaped cross section, whereby the spring-back can besufficiently prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing steps of obtaining a final formed article froma blank by a press forming method as an embodiment of the presentinvention;

FIG. 2 is a view showing a first step in the press forming method shownin FIGS. 1 ; and

FIG. 3 is a view showing a second step in the press-forming method shownin FIG. 1 .

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention will be described below withreference to the drawings. FIG. 1 is a view showing steps of obtaining afinal formed article from a blank by a press-forming method as anembodiment of the present invention. In FIG. 1 , an upper stage shows afinal formed article 1 in a transverse manner, and a lower stage shows aprogress of a process phase from left to right in a transverse manneralong with a cross-sectional view of the final formed article 1. A phaseis denoted as PO in which a supplied blank 2 is unprocessed.

A phase is indicated by P1 in which a preformed article 30 in a firstform is obtained by a first step. A phase is indicated by P2 in which apreformed article 40 in a second form is obtained by a second step.Phases are indicated by P3 and P4 in which the final formed article 1 isobtained by a third step.

The final formed article 1 has a hat-shaped cross section. A site of thefinal formed article 1 having the hat-shaped cross section includes atop surface 3 and a left vertical wall 4 and a right vertical wall 5continuing to left and right ends of the top surface 3. Furthermore, thesite of the final formed article 1 having the hat-shaped cross sectionincludes a left flange 6 and a right flange 7 extending from a lower endof the left vertical wall 4 and a lower end of the right vertical wall5, respectively. In addition, the site of the final formed article 1having the hat-shaped cross section includes a left bent portion 8interposed between the left vertical wall 4 and the left flange 6 and aright bent portion 9 interposed between the right vertical wall 5 andthe right flange 7.

FIG. 2 is a view showing the first step. The first step is a processingstep of the phase P1 in FIG. 1 . In the first step, from the blank 2,the preformed article 30 in the first form is obtained which includes atop surface 33 in a first form, a left vertical wall 34 in a first form,a right vertical wall 35 in a first form, and a left tapered portion 31and a right tapered portion 32 in a first form extending respectivelyoutward (downward in FIG. 2 ) from lower ends of the left vertical wall34 in the first form and the right vertical wall 35 in the first form.

The first step includes processing steps of a phase P11, a phase P12,and a phase P13. Hereinafter, the processing steps of the phase P11, thephase P12, and the phase P13 are simply referred to as a phase P11, aphase P12, and a phase P13. The preformed article 30 in the first formis shown in the phase P13.

In the phase P11, an edge of the blank 2 is clamped and fixed in a stateof being pressed against a first upper die 11 by a blank holder 10. Inthis state, a projection 12 a on an upper side of a first lower punch 12contacts a lower surface of the blank 2, but a movable pad 13 on a sideof the first upper die 11 does not contact an upper surface of the blank2.

Next, in the phase P12, the first upper die 11 is lowered together withthe movable pad 13 in a state where the blank 2 is held by the blankholder 10. At this time, the movable pad 13 is brought into contact withand pressed from above against a site of the blank 2 supported by anupper end surface of the first lower punch 12 including the projection12 a.

Next, in the phase P13, the first upper die 11 is lowered in the statewhere the contact site on the blank 2 side is held with the movable pad13 brought into contact with and pressed from above. The preformedarticle 30 in the first form is obtained in such a processing step ofphase P13. In the phase P13, the top surface 33 in the first formcorresponding to the top surface 3 of the final formed article 1 isformed. Further, when ends of the blank 2 are pressed by the first upperdie 11 and a left inclined portion 12 b and a right inclined portion 12c having inclined surfaces which are outwardly inclined below the firstlower punch 12, respectively, the left tapered portion 31 and the righttapered portion 32 are formed.

FIG. 3 is a view showing the second step. The second step is theprocessing step of the phase P2 in FIG. 1 . In the second step, in astate where the top surface 33 in the first form of the preformedarticle 30 in the first form is held by an upper die and a punch of alower die, the left tapered portion 31 and the right tapered portion 32are pushed into recesses for curling forming provided in a lower die toform left and right bent portions, and left and right flanges are formedby lowering of the upper die, whereby a preformed article 40 in a secondform is obtained.

Next, a more specific description will be given. The second stepincludes processing steps of a phase P21, a phase P22, and a phase P23.Hereinafter, the processing steps of the phase P21, the phase P22, andthe phase P23 are simply referred to as a phase P21, a phase P22, and aphase P23, respectively. The preformed article 40 in the second form isshown in the phase P23.

In the phase P21, the top surface 33 in the first form of the preformedarticle 30 in the first form is held by a second upper die 14 as anupper die and a floating punch 16 of a second lower die 15 as a lowerdie. In other words, the top surface 33 in the first form is pressedagainst the second upper die 14 by the floating punch 16 and is adjustedin posture. At this time, the left tapered portion 31 of the preformedarticle 30 in the first form hangs down from a lower end of the secondupper die 14 toward a left recess 17 for curling forming of the secondlower die 15. Similarly, the right tapered portion 32 of the preformedarticle 30 in the first form hangs down from the lower end of the secondupper die 14 toward a right recess 18 for curling forming of the secondlower die 15.

Next, in the phase P22, the second upper die 14 is lowered, and the lefttapered portion 31 of the preformed article 30 in the first form ispushed into the left recess 17 of the second lower die 15 from a hangingend thereof. Similarly, the right tapered portion 32 of the preformedarticle 30 in the first form is pushed into the right recess 18 of thesecond lower die 15 from a hanging end thereof. At this time, the lefttapered portion 31 and the right tapered portion 32 are formed so as toextend outward, and move along R-shaped surfaces of the left recess 17and the right recess 18 to be curled.

Next, in the phase P23, the second upper die 14 is lowered to a bottomdead center. In the course of the lowering, the left tapered portion 31is pinched between the second upper die 14 and the second lower die 15,and is formed into a left vertical wall 44 in a second form, a left bentportion 48 in a second form, and a left flange 46 in a second form ofthe preformed article 40 in the second form. At the same time, the righttapered portion 32 is pinched between the second upper die 14 and thesecond lower die 15, and is formed into a right vertical wall 45 in asecond form, a right bent portion 49 in a second form, and a rightflange 47 in a second form of the preformed article 40 in the secondform.

In the course of transition from the phase P22 to the phase P23, theleft vertical wall 34 of the preformed article 30 in the first form ispushed into the left recess 17 of the second lower die 15 and is curled.At the same time, the right vertical wall 35 of the preformed article 30in the first form is pushed into the right recess 18 of the second lowerdie 15 and is curled.

Therefore, a sufficient compressive force can be applied to a part in awide range from the left vertical wall 44 in the second form to the leftbent portion 48 in the second form and the left flange 46 in the secondform. At the same time, a sufficient compressive force can be applied toan entire wide range from the right vertical wall 45 in the second formto the right bent portion 49 in the second form and the right flange 47in the second form. Therefore, spring-back of the final formed article 1is prevented.

As described above, in the processing step up to the phase P2 throughthe phase P1 in FIG. 1 , a pressing force f1 is applied to the formedarticle having a shape and dimensions close to those of the final formedarticle 1 in the phase P3 such that the final shape and dimensions ofthe top surface 43 as the wavy surface are obtained, and thus the formedarticle is deformed. Further, in the phase P4, pressing forces f2 and f3are applied to the left vertical wall 44 and the right vertical wall 45to strictly adjust a separation dimension between the left vertical wall44 and the right vertical wall 45, and further, the left flange 46 andthe right flange 47 are reformed by trimming or the like, whereby thefinal formed article 1 having the hat-shaped cross section is obtained.The phase P3 and the phase P4 correspond to the third step of reformingthe left bent portion 48, the right bent portion 49, the left flange 46,and the right flange 47 of the preformed article 40 in the second formand obtaining the final formed article 1 having the hat-shaped crosssection. After the third step, the final formed article 1 is delivered.

According to the press-forming method of the present embodiment, thefollowing effect is obtained.

In the press-forming method according to (1) described above, thepreformed article 30 in the first form is obtained from the blank 2 inthe processing step of the phase P1 which is the first step, thepreformed article including the top surface 3, the left vertical wall 4,the right vertical wall 5, and the left tapered portion 31 and the righttapered portion 32 extending respectively outward from the lower ends ofthe left vertical wall 4 and the right vertical wall 5 in the finalformed article 1 having the hat-shaped cross section. In the processingstep of the phase P2 which is the second step, the left tapered portion31 and the right tapered portion 32 are pushed into the left recess 17and the right recess 18 for curling forming provided in the second lowerdie 15 in the state where the top surface 33 of the preformed article 30in the first form is held by the second upper die 14 and the floatingpunch 16 of the second lower die 15, thereby forming the left bentportion 48 and the right bent portion 49, and the left and right flangesare formed by the lowering of the second upper die 14 to obtain thepreformed article 40 in the second form. In the processing steps of thephase P3 and the phase P4 which are the third step, the left bentportion 48, the right bent portion 49, the left flange 46, and the rightflange 47 of the preformed article 40 in the second form are reformed toobtain the final formed article 1 having the hat-shaped cross section.From the phase P22 to the phase P23, which are steps of obtaining thepreformed article of the preformed article 40 in the second form in theprocessing step of the phase P2 which is the second step, thecompression can be applied to the entirety of the top surface 3, theleft vertical wall 4, the right vertical wall 5, the left flange 6, andthe right flange 7 of the final formed article 1 having the hat-shapedcross section, whereby the spring-back can be sufficiently prevented.

Although the embodiment of the present invention has been describedabove, the present invention is not limited thereto. Detailedconfigurations may be changed as appropriate within the scope of thepresent invention. For example, the top surface 3 is a wavy surface withthe projection only on the left vertical wall 4 in the above-describedexample, but may be a wavy surface with a projection on the rightvertical wall 5.

EXPLANATION OF REFERENCE NUMERALS

1 . . . final formed article

2 . . . blank

30 . . . preformed article in first form

40 . . . preformed article in second form

3 . . . top surface

4 . . . left vertical wall

5 . . . right vertical wall

6 . . . left flange

7 . . . right flange

8 . . . left bent portion

9 . . . right bent portion

10 . . . blank holder

11 . . . first upper die

12 . . . first lower punch

12 a . . . projection

12 b . . . left inclined portion

12 c . . . right inclined portion

13 . . . movable pad

14 . . . second upper die

15 . . . second lower die

16 . . . floating punch

17 . . . left recess

18 . . . right recess

30 . . . preformed article in first form

31 . . . left tapered portion

32 . . . right tapered portion

40 . . . preformed article in second form

What is claimed is:
 1. A method of press-forming, from a blank, a finalformed article having a hat-shaped cross section and including a topsurface, left and right vertical walls continuing to left and right endsof the top surface, left and right flanges extending from lower ends ofthe left and right vertical walls, respectively, and left and right bentportions interposed respectively between the left vertical wall and theleft flange and between the right vertical wall and the right flange,the press-forming method comprising: a first step of obtaining, from theblank, a preformed article in a first form including the top surface,the left and right vertical walls, and left and right tapered portionsextending outward from the lower ends of the left and right verticalwalls, respectively; a second step of forming the left and right bentportions by, in a state where the top surface of the preformed articlein the first form is held by an upper die and a punch of a lower die,pushing the left and right tapered portions into recesses for curlingforming provided in the lower die and forming the left and right flangesby lowering of the upper die to obtain a preformed article in a secondform; and a third step of obtaining the final formed article having thehat-shaped cross section by reforming the left and right bent portionsand the left and right flanges of the preformed article in the secondform.